1. Field of Invention
This invention mainly provides a SMT-type structure of the silicon-based electret condenser microphone. Primarily integrates the electret technology, silicon-based, MEMS and microphone to form the SMT-type silicon-based electret condenser microphone.
2. Description of the Prior Art
As the technology has made great progress nowadays, the size of mobile communication device becomes smaller and smaller indeed. Correspondingly, its whole module and the internal electronic parts must be minimized as much as possible. The traditional condenser microphone not only owns a larger dimension, but also costs a lot. It needs higher voltage bias for driving it to work with; therefore it is not satisfied with the requirement of the mobile communication device, which specifies under a lower voltage and a smaller volume. Considering the tiny mobile communication device that owns high efficiency, how to minimize the microphone becomes necessary and urgent.
The microphone is a mechanism using to transfer the sound energy into the electrical energy. Usually, there are dynamic microphone, condenser microphone, piezoelectric/piezoresistive microphone and electret condenser microphone. As far as we know, U.S. Pat. No. 5,490,220 describes a solid-state condenser microphone, which needs very high polarized-voltage input and is very sensitive to humidity. It requires a specified moisture-proof storage to keep it. Secondly, U.S. Pat. No. 5,740,261 describes a microphone structure, which needs more than 10 volts to acquire a better sensitivity, and it can't be minimized and worked with low-power usage. Furthermore, U.S. Pat. Nos. 6,012,335, 5,573,679, 5,889,872 and 5,888,845 mention that the microphone, which has concise structure with a mono-chip implementation. If people want to upgrade it to a bi-chip product, he has to consider how to construct its complex structure, and the time span of the process shall be expanded with higher techniques.
The traditional condenser microphone comprises a thin film and a fixed substrate, and then capacitor will be formed with a specified gap between this thin film and the fixed substrate. Whenever the outsider sound pressure makes the film vibration to generate the displacement variation under a polarized-voltage applied on that thin-film, the capacitance varied to generate a current signal, which is followed with the sound pressure rationally. However, this type's condenser microphone requires the external power to support the microphone response for sensing the sound pressure varying as the capacitance effects. Therefore it needs a higher polarized-voltage input to acquire a better sensitivity, but the elongation of thin film can't be uniformly distributed and the thin film is very sensitive to the environmental humidity.